1. Field of the Invention
The present invention relates generally to frequency tracking systems in radar receivers and more particularly to a system for acquiring and tracking a variable frequency signal with a local oscillator while preventing a false lock of the local oscillator on an incorrect e.g. a image frequency, instead of the correct frequency, and while holding the loop bandwidth substantially constant.
2. Description of the Prior Art
Typically, a phase lock loop for radar applications includes a stable, crystal controlled microwave reference source, a VHF crystal offset oscillator, and a microwave voltage controlled oscillator (VCO) which is phase locked to the crystal references. Such loops have been and continue to be plagued with two distinct types of problems, namely, false locking and variations in loop bandwidth due to RF power variation and non-linearity in the tuning characteristic of the VCO.